1. Field of the Invention
The invention relates to a ceramic heater, for example, suitable for a system for producing semiconductors.
2. Related Art Statement
In a system for producing semiconductors, a ceramic heater may be provided for heating a wafer so as to deposit a semiconductor thin film on the wafer from gaseous raw materials such as silane gas by means of thermal CVD or the like. In such a ceramic heater, it is required to make the temperature of the heating face and the semiconductor wafer mounted thereon uniform with high precision.
Several techniques for reducing the temperature distribution on the heating (mounting) face of the ceramic heater are known. For example, a so-called two-zone heater is known. Such a two-zone heater includes a ceramic substrate and inner and outer resistance heat generators embedded in the substrate. Separate power supply terminals are connected to the respective heat generators so that electric power may be applied independently on the respective generators. Heat generated from the inner and outer heat generators may be thus independently controlled.
Such a two-zone heater includes the following. Japanese patent publication 2001-102157A discloses a heater having a ceramic substrate and two layers of heating elements embedded in the substrate. The calorific values in the inner zone and outer zone of each heating element are controlled so that two-zone control system of inner and outer zones may be realized.